1. Field of the Invention
This invention relates to ink jet printing systems, and in particular to an ink curing apparatus system to insure the uniform solidification of jetted ink on the paper to which it is applied.
2. Background of the Invention
Ink jet printers are becoming an increasing popular type of device for recording permanent images on paper. Ink jet printers operate by directing a stream of minute ink droplets at the paper so as to produce a distinct pattern of individual ink dots. By selectively depositing ink dots on paper, and by regulating the number of dots discharged onto the paper, an ink jet printer can be used to create almost any type of print: text; graphics; or images. This capability has made it attractive to attach ink jet printers to computer systems that produce both figurative and textual output simultaneously. This is because a properly programmed ink jet printer can be used to produce a complicated figure and a detailed description of the figure on the same page.
Moreover, many ink jet printers are capabile of discharging multiple colors of ink so as to generate quality color figures and and illustrations. This capabilty has contributed to their popularity since computer systems that can generate multi-color video output in the form of figures and images are becoming increasingly common. These computer systems require printing devices that can produce permanent images of the output they generate.
In the past, many ink jet printers have discharged liquid ink onto the paper. Some of these inks have caused problems because of their continual tendency to wick or bleed onto the paper, thus significantly blurring the optical edges of the individual ink dots. This blurring has significantly reduced the quality of the overall images they produce. Moreover, this blurring has made it extremely difficult to use liquid inking systems with printers discharging multiple colors of ink since the individual dots of different color blend together, so as to substantially distort the final image.
To overcome the problem of ink wicking and subsequent dot bluring, a number of ink jet printers rely on a heated or "hot-melt" inking systems such as the one disclosed in U.S. Pat. No. 3,247,519, dated Apr. 19, 1966 to Sihvonen for a Graphical Recording System Employing Heated Ink Compositions. The advantage of hot melt ink is that it solidifies relatively quickly as soon as it is deposited on the paper. This reduces the bleeding, or wicking, of ink on the paper so each ink dot has a well defined optical edge, and the final image has distinct features.
However, even when ink is discharged from a hot-melt inking system, there may be a tendency for some of the ink droplets to soak through or wick on the paper before it solidifies. Ink soak-in is likely to happen at locations on the paper where very dark images are produced, or multiple layers of ink are applied, and large amounts of ink must be applied. Some of the ink may soak into the paper, or may wick through through it due to the capillary action of paper's fiber structure. This soak-in and wicking will cause blurring of the optical edges of the individual ink dots, and cause the quality of the overall image produced to be degraded.
Moreover, many ink jet printers discharge ink that solidifies at different rates on the paper it is deposited on. This may be a problem for many inks because their final solid appearance is directly related to their crystalline structure, which is a function of the rate at which they solidify. Some inks, for example, if they solidify quickly, have a glossy appearance. If the same inks solidify slowly, they appear matted. If all the ink on a page does not solidify at a uniform rate, some of it may appear matted and some of it may appear glossy. As a result, the final image produced on the page may have an inconsistent and anaesthetic appearance.
Furthermore, some inks have a low physical strength and a poor ability to cling the paper they discharged onto. If these inks cure too quickly, their low clinging ability may be further reduced. This may cause the ink to crack or flake off the paper when it is bent or folded, reducing the image quality or possibly lossing information.
In ink jet printers it is desirable to securely position the paper a small distance away from the printing jets. Many printers rely on a relatively expensive, accurately positioned mechanical holding mechanism to do this. If the mechanism is distorted, such as may happen through wear or accidentally bending, the paper may not be properly seated in relationship to the ink jets. If this happens, when ink is applied to the paper, it will be in the wrong location and the resulting image may not accurately depict what it was intended to show.